Rearrangements of delta-, tau-, and beta- T-cell receptor (TcR) chain genes were analysed in 64 haematologic malignancies comprising T- and B-lineage acute lymphoblastic leukaemias (ALL), B-chronic lymphocytic leukaemias (CLL), acute myeloid leukaemias (AML) and acute undifferentiated leukaemias AUL). The TcR genes were rearranged in 5/6 T-ALL. In non-T-leukaemias the frequency of TcR gene rearrangements was higher in B-lineage ALL (8/11), although they were all detected in B-CLL (5/29), AML (1/16) and AUL (2/4). Immunoglobulin (Ig) gene rearrangements were observed in 1/6 T-ALL and 2/14 AML. The analysis of these gene configurations has a diagnostic application since it allows the definition of the clonality of malignant proliferation and although they are not lineage specific such configurations represent a further parameter to evaluate, together with the immunophenotype and morphology, in the assignment or exclusion of the differentiation lineage of the haematologic malignancies.